Just to add to what CJW was saying about BOR, a more extreme example is DN class ice boats. When they round thier top mark and head "downwind" they only ease about a foot of sheet. They do travel at over 100km hour though.
A) A river flows south at 10 knots. The wind is blowing from the North at 10 knots.
B) A river flows south at 10 knots. There is no wind.
You want to sail South down the river. Which of the above will get you there faster?
Neither - same speed
For A there is no apparent wind (you are just drifting with current in both examples)
Interesting to listen in..you guys certainly have more analytical minds than me..I suppose I do err on the creative side though..
Yeah Bs correct.
You have 10 knots of apparent head wind to deal with so if you can sail upwind in 10 knots you're ahead of the game.
Maybe B is correct? You are sailing directly downwind and down current.
With A, the current will make you travel downwind with no air resistance so you will do 10kn... exactly 10kn.
With B, the current will try to make you sail downwind at 10kn but due to the apparent headwind, a correct sheeting angle will make power and you'll go faster.
So depends on the resistance of the hull and efficiency of the rig 
Dude, get off ya high horse, I can land double loops no hands, and often no feet, all day long
Dunno frant "sailing close hauled" is fine but the question requires to you to travel due south not close to it
B, as long as you are allowed to sail i.e. take what ever course you need, in order to arrive due south (which I believe the question allows). You would need to make an even number of close reaches (upwind), ideally two.
You all have convinced me. Is there any theoretical explanation of this effect on the net ?. I researched this topic last year, but found very little and none of this was from researchers.
I understood there was more to it than just the relative wind on the water. ie. a 20 knot wind into a 3 knot tide produces far more chop than a 26 knot wind going with a 3 knot tide. Bit I'm not sure, maybe it is just observations that don't allow for the relative wind.
It IS possible to sail with a conventional type sail at speeds in excess of the wind speed. It is also possible to sail with a conventional type sail at a VMG downwind at greater than the wind speed. A windsurfer is capable of approx 2 x windspeed at 90 deg to the true wind and pretty close to VMG downwind of windspeed at 135 deg to to the true wind. The latest AC craft easily exceeded these numbers. My definition of a conventional sail includes wing sails but excudes turbines that drive a water propellor or those little wheeled craft that use their wheels to drive an air propellor. A turbine driven water propelled craft can "sail" directly upwind. The little wheeled craft can extract energy from the wind whilst travelling directly down wind at greater than true wind speed and thus "sail" directly downwind at greater than true wind speed.
With a conventional sail apparent wind provides no drive to the craft and only limits the speeds that can be achieved, it is only the true wind which provides thrust. Apparent wind is made up of the vector sum of true wind plus speed wind.
Speed wind is from dead ahead and therefore does not provide any forward thrust (only slows or restricts speed, drag). True wind provides the only forward thrust. The sails must be trimmed for apparent wind, as the speed of the craft increases the apparent wind moves forward and the sails must be trimmed in. With a windsurfer after the initial acceleration where the sails are trimmed it is possible to vary your course from approx 45 deg to wind to 135 deg to wind without trimming the sail from a close sheeted position. Your speed will adjust automatically so that the apparent wind is always from the same direction.
The illustrution of how it is possible to make a VMG downwind of greater than the true wind speed are most easily explained with vector diagrams. Might do some sketches and scan them in later.
